THE LURE OF ULURU

In a classic example of understatement, most Australians simply call it “The Rock.” Rising 1,142 feet in awesome and solitary grandeur above the surrounding flat desert, it is one of the world’s best-known natural features. It’s also a sacred site representing 30,000 years of human habitation and an iconic image of Australia and that nation’s vast Outback. Previously called Ayers Rock, “The Rock” is today known as Uluru (ool-a-roo), a name of great antiquity that even predates the Ice Ages.

- STEVE VOYNICK

A rainbow, rare in the arid Outback, appears above Uluru at sunrise.

TECTONIC ORIGIN

Geologically speaking, Uluru is an inselberg (“island mountain” in German), a small, isolated mountain that rises abruptly from a level plain. Inselbergs consist of hard, resistant rocks that erode much more slowly than the surrounding rocks.

Uluru’s geological story began 550 million years ago with a major, tectonically driven mountain-building event called the Peter-mann Ranges Orogeny. The original mountains of the Petermann Ranges approached The scale of today’s Himalayas. But because trees and grasses did not yet exist when the Petermann Ranges were uplifted, erosion progressed rapidly.

In this 2015 photograph, hikers head toward the summit of Uluru; climbing the monolith was banned in 2019, and the chain handhold was removed.

After enormous amounts of sediments from these eroded mountains created vast alluvial fans, a shallow sea covered the region, burying the fans beneath thick layers of marine sediments. Under great pressure, one thick, sandy stratum of an alluvial fan lithified into sandstone of unusual hardness and durability.

A later tectonic event, the Alice Springs Orogeny, raised the region above sea level, folded the buried sandstone, and tilted its alignment from horizontal to nearly vertical. The surface then eroded quickly, with the exception of that unusually hard and durable stratum that today rises above the flat desert floor as Uluru. Uluru consists of an arkose (potassium feldspar-rich) sandstone. When freshly broken, it is gray in color, although its surface is always rusty reddish-brown due to the presence of hematite (iron oxide).